Re: [SQLObject] Expiring Cache

[Ian B. <ia...@co...>]

On Monday, October 27, 2003, at 02:12 PM, Sidnei da Silva wrote:
> Howdy again,
>
> I am in the process on getting the Zope3+SQLObject integration to the
> next level, which is optimization. I haven't started profiling yet,
> but one of the things that I would like to try is to enable cache on
> SQLObject (I disabled it since the start because it was getting too
> much in the way) and hook with the event system in Zope 3 to process
> cache invalidation when an ObjectModified message comes
> through. However I am not sure about the way the SQLObject.expired()
> method is implemented. It seems that it is doing a bit more than
> expiring the cache, it is also marking the object as expired and
> removing something from the instance which I'm not sure what it
> is. The way I see it, I should probaly call expired() which would
> mark the object as expired and clear the cache for that object. On the
> first attribute access after that, SQLObject would find the cache is
> empty, fetch the live values from database and remove the expired mark
> from the object. Maybe a revalidate() method on SQLObject could do it,
> to make it simpler. Am I close?

SQLObject.expire() expires the *instance's* cache of its column values. 
  When you create an instance, it gets its column values from the 
database immediately.  When a transaction is rolled back we expire all 
the effected instances' caches so that they don't contain stale 
information from a rolled-back transaction.  (There perhaps should be 
other circumstances where we automatically expire instances, but I 
haven't thought that through).

The per-connection cache is a different issue.

I'm not sure what SQLObject should do for an ObjectModified message.  
What does this message mean?  There's also the issue of non-column 
instance variables (which you might manually add to a SQLObject 
subclass) and rolling those values back... that might be related, or 
maybe you are avoiding that issue entirely for the moment.

--
Ian Bicking | ia...@co... | http://blog.ianbicking.org